1. Field of the Invention
This invention relates in general to an electronically controlled embroidering machine capable of producing a desired embroidery pattern on a fabric supported within an embroidery frame. This invention is particularly directed to a control system for shifting under control the embroidery frame in the embroidering machine of the aboveidentified type.
2. Description of the Prior Art
An electronically controlled embroidering machine includes, as known, a needle connected to an upper drive shaft to reciprocate in a vertical direction in synchronism with rotation of the upper drive shaft which is driven by a machine motor, an embroidery frame detachably supported to the machine housing and a loop-taker means cooperating with the needle to form a stitch on a fabric supported in a stretched condition within the embroidery frame. The embroidery frame is stepwise shiftable in two perpendicular directions (X- and Y-directions) by respective pulse motors so that a relative position between the needle and the fabric may be obtained as desired. Embroidery pattern data for a plurality of embroidery patterns will be stored in a memory and selectively read out for controllably driving the machine motor and the pulse motors to thereby produce a selected embroidery pattern on the fabric.
The embroidery frame is shifted while the machine motor is rotating to actually produce the selected embroidery pattern. The embroidery frame will also be activated during suspension of the machine motor, for example in the following operations:
1) Initial position determining operation in which the embroidery frame is shifted to a predetermined initial position relative to the needle once the embroidering machine is energized.
2) Manual shift operation in which the embroidery frame is shifted to a desired position relative to the needle for producing the selected embroidery pattern on the fabric in a desired area or region thereof.
3) Stitch area confirming operation in which, prior to the actual embroidering operation, the embroidery frame is shifted in response to the pattern control data of the selected embroidery pattern, with the machine motor being kept standstill, for the purpose of confirming that the selected embroidery pattern may surely be produced within an area of the fabric defined and coutoured by the embroidery frame. 4) Frame forward/back operation in which, when it is found at a certain stitch point that the stitch has been produced out of order or deformed at a previous stitch point, the embroidery frame is shifted back to the said previous stitch point so that such imperfect stitch is repaired by re-embroidering (in the frame back operation), and after that the embroidery frame is returned to the certain stitch point for re-starting subsequent embroidering operation (in the frame forward operation).
The initial position determining operation should not be carried out when the needle penetrates the fabric. To cope with this, the conventional system is provided with a sensor means which detects the vertical needle position relative to the fabric. If the needle should be currently positioned in contact with the fabric, which is discriminated by the sensor as "shift-prohibited circumstance", the initial position determining operation will be preceded by some rotation of the machine motor to separate the needle above from the fabric.
However, it is to be noted in this connection that the embroidery frame has a peripheral edge which upstands higher than a level of the fabric stretched within the frame and overlying the needle plate. Even when the needle tip end is located above the fabric but below the top of the peripheral edge of the embroidery frame and the current horizontal position of the needle is not within an area defined by the embroidery frame, this could not be detected as the "shift prohibited circumstance" in the conventional system, with the result that no preceding operation for the machine motor rotation is carried out. If the initial position determining operation should be commenced in this particular circumstance, the peripheral edge of the embroidery frame would come into contact with the needle and/or the presser foot while shifting the embroidery frame, which may break the needle and result in mechanical troubles.
In the stitch area confirming operation, the operator will be desirous to lower the needle to a position just above the fabric for easier confirmation of the stitch area. This can be achieved by manually rotating to a certain degree a flywheel connected directly to the upper drive shaft. However, since the flywheel may be freely rotated even by slight touching, there has been a tendency that the flywheel is overrotated to cause the needle to penetrate the fabric while the embroidery frame is shifting in the stitch area confirming operation. This would result in breakage of the needle and fatal damage of the fabric.